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We report a case of bilateral ptosis due to paramedian midbrain infarction, which was associated with ipsilateral impaired adduction of the eye and contralateral ataxia. T2-weighted magnetic resonance imaging of the brain revealed a right paramedian midbrain infarction. The ptosis rapidly improved without a difference between the left and right sides, while the other symptoms mostly resolved within a month following treatment with antiplatelet agents and rehabilitation. An infarction of the paramedian dorsocaudal portion of the midbrain can involve both the central caudal nucleus and the median longitudinal fasciculus (MLF), causing a peculiar combination of symptoms, bilateral ptosis, and unilateral MLF syndrome.

Previous studies have revealed unexpected relationships between the firing rates of horizontally acting motoneurons and vergence. During a vergence task, for example, antidromically identified abducens internuclear neurons show a negative correlation between vergence angle and firing rate, which is the opposite of the modulation displayed by the medial rectus motoneurons to which they project. For a given horizontal eye position, medial rectus motoneurons discharge at a higher rate if the eyes are converged than if the same eye position is reached during a task that requires version; paradoxically, however, the horizontal rectus eye muscles show corelaxation during vergence. These complex and unexpected relationships inspired the present author to investigate whether the tonic firing rates of vertically acting motoneurons in oculomotor nucleus are correlated with vergence angle. Monkeys were trained to fixate a single, randomly selected, visual target among an array of 60 red plus-shaped LEDs, arranged at 12 different distances in three-dimensional space. The targets were arranged to permit dissociation of vertical eye position and vergence angle. Here I report, for the first time, that most vertically acting motoneurons in oculomotor nucleus show a significant negative correlation between tonic firing rate and vergence angle. This suggests the possibility that there may be a general corelaxation of extraocular muscles during vergence. NEW & NOTEWORTHY An array of 60 plus-shaped LEDs, positioned at various locations in three-dimensional space, was used to elicit conjugate and disjunctive saccades while single neurons in oculomotor nucleus were recorded from rhesus monkeys. This study demonstrates that most vertically acting motoneurons in oculomotor nucleus discharge at a lower rate when the eyes are converged. [ABSTRACT FROM AUTHOR]

We report a case of bilateral ptosis due to paramedian midbrain infarction, which was associated with ipsilateral impaired adduction of the eye and contralateral ataxia. T2-weighted magnetic resonance imaging of the brain revealed a right paramedian midbrain infarction. The ptosis rapidly improved without a difference between the left and right sides, while the other symptoms mostly resolved within a month following treatment with antiplatelet agents and rehabilitation. An infarction of the paramedian dorsocaudal portion of the midbrain can involve both the central caudal nucleus and the median longitudinal fasciculus (MLF), causing a peculiar combination of symptoms, bilateral ptosis, and unilateral MLF syndrome. [ABSTRACT FROM AUTHOR]

AIM: To make an electrophysiological demonstration of a possible jaw muscle afferents-oculomotor neural pathway that was proposed by our previous works on rats, which substantiates an early “release hypothesis” on pathogenesis of human Marcus Gunn Syndrome (MGS). METHODS: Extracellular unit discharge recording was applied and both orthodromic and spontaneous unitary firing were recorded in the oculomotor nucleus (III), and the complex of pre-oculomotor interstitial nucleus of Cajal and Darkschewitsch nucleus (INC/DN), following electric stimulation of the ipsilateral masseter nerve (MN) in rats. RESULTS: Extracellular orthodromic unit discharges, with latencies of 3.7±1.3 and 4.7±2.9ms, were recorded unilaterally in the III, and the INC/DN neurons, respectively. Spontaneous unit discharges were also recorded mostly in the INC/DN and less frequently in the III. Train stimulation could prompt either facilitation or inhibition on those spontaneous unit discharges. The inhibition pattern of train stimulation on the spontaneous discharging was rather different in the III and INC/DN. A slow inhibitory pattern in which spontaneous firing rate decreased further and further following repeated train stimulation was observed in the III. While, some high spontaneous firing rate units, responding promptly to the train stimuli with a short-term inhibition and recovered quickly when stimuli are off, were recorded in the INC/DN. However, orthodromic unit discharge was not recorded in the III and INC/DN in a considerable number of experiment animals. CONCLUSION: A residual neuronal circuit might exist in mammals for the primitive jaw-eyelid reflex observed in amphibians, which might not be well-developed in all experimental mammals in current study. Nonetheless, this pathway can be still considered as a neuroanatomic substrate for development of MGS in some cases among all MGS with different kind of etiology.

Amyotrophic lateral sclerosis (ALS) is a progressive multifactorial disease characterized by the loss of motor neurons (MNs). Not all MNs undergo degeneration: neurons of the oculomotor nucleus, which regulate eye movements, are less vulnerable compared to hypoglossal nucleus MNs. Several molecular studies have been performed to understand the different vulnerability of these MNs. By analyzing postmortem samples from ALS patients to other unrelated decedents, the differential genomic pattern between the two nuclei has been profiled. Among identified genes, adenylate cyclase activating polypeptide 1 (ADCYAP1) gene, encoding for pituitary adenylate cyclase-activating polypeptide (PACAP), was found significantly up-regulated in the oculomotor versus hypoglossal nucleus suggesting that it could play a trophic effect on MNs in ALS. In the present review, some aspects regarding the different vulnerability of oculomotor and hypoglossal nucleus to degeneration will be summarized. The distribution and potential role of PACAP on these MNs as studied largely in an animal model of ALS compared to controls, will be discussed.

Lower motoneurons (MNs) show varied vulnerability in amyotrophic lateral sclerosis (ALS): those of non-ocular brainstem nuclei and most of those of the spinal cord are highly vulnerable, while those of extraocular brainstem nuclei are quite resistant. Results of our former study on the immunoexpression of the survival of motor neuron protein (SMN) and Gemins 2-4 in cervical spinal cord anterior horn -MNs of sporadic ALS patients suggested that a relative deficit in Gemin2 may play some role in the pathomechanism of the disease. Here, we tested this idea further by comparing immunoexpression patterns of SMN and Gemins 2-8 between MNs of the oculomotor nucleus and -MNs of the cervical spinal cord anterior horns in autopsy material from sALS patients and controls. In the latter, no considerable difference in any studied protein was found between these structures except that SMN expression was slightly but significantly lower (p < 0.01) in the oculomotor MNs. In the sporadic ALS patients, the expression of SMN, Gemin4 and Gemin7 was significantly weaker (p < 0.05, p < 0.05 and p < 0.01, respectively), while that of Gemin8 was stronger (p < 0.001) in the MNs of the oculomotor nucleus than in the examined cervical spinal cord anterior horn -MNs. The immunoexpression of Gemin3 and Gemin6 in the spinal cord correlated strongly negatively with ALS duration (Spearman’s correlation coefficient: RS = –0.84, p < 0.001, and RS = –0.86, p = 0.002, respectively). In the oculomotor nucleus MNs, no studied protein immunoexpression correlated significantly with ALS duration, but there was a tendency for such negative correlation for Gemin2 (RS = –0.56, p = 0.07). There was an apparent relative deficit of Gemin2 and Gemin8 in the spinal cord -MNs and of Gemins 2, 4 and 7 in the oculomotor nucleus MNs. These data do not support the hypothesis that the diverse ALS vulnerability of the two MN subsets is related to their disparate expression patterns of SMN and Gemins 2-8. The differences in these patterns may result from ALS-related epiphenomena, or from intrinsic differences in the structure and function between the MN subsets, or both.

The morphology of the motor divisionof oculomotor nucleus in the buffalo has been described by materials collected from eight buffalos. Myelin stained serial and semi serial sections of brain stem were used for the study. The motor nucleus of oculomotor nerve was located ventral to the cerebral aqueduct in a wedge shaped trough formed by the medial longitudinal fasciculus. It extended from the level of junction of the rostral and caudal colliculi to the cranial third of the rostral colliculus. The average length, width and height of the motor nucleus in the buffalo were 8.1mm, 1.75mm and 2.75mm respectively. The motor nucleus in the buffalo was subdivided into a caudal central, dorsomedial, dorsolateral and ventral divisions.

Amyotrophic lateral sclerosis (ALS) is a progressive multifactorial disease characterized by the loss of motor neurons (MNs). Not all MNs undergo degeneration: neurons of the oculomotor nucleus, which regulate eye movements, are less vulnerable compared to hypoglossal nucleus MNs. Several molecular studies have been performed to understand the different vulnerability of these MNs. By analyzing postmortem samples from ALS patients to other unrelated decedents, the differential genomic pattern between the two nuclei has been profiled. Among identified genes, adenylate cyclase activating polypeptide 1 (ADCYAP1) gene, encoding for pituitary adenylate cyclase-activating polypeptide (PACAP), was found significantly up-regulated in the oculomotor versus hypoglossal nucleus suggesting that it could play a trophic effect on MNs in ALS. In the present review, some aspects regarding the different vulnerability of oculomotor and hypoglossal nucleus to degeneration will be summarized. The distribution and potential role of PACAP on these MNs as studied largely in an animal model of ALS compared to controls, will be discussed. [ABSTRACT FROM AUTHOR]

Many animal studies have reported on the neural connectivity of the vestibular nuclei (VN). However, little is reported on the structural neural connectivity of the VN in the human brain. In this study, we attempted to investigate the structural neural connectivity of the VN in 37 healthy subjects using diffusion tensor tractography. A seed region of interest was placed on the isolated VN using probabilistic diffusion tensor tractography. Connectivity was defined as the incidence of connection between the VN and each brain region. The VN showed 100% connectivity with the cerebellum, thalamus, oculomotor nucleus, trochlear nucleus, abducens nucleus, and reticular formation, irrespective of thresholds. At the threshold of 5 streamlines, the VN showed connectivity with the primary motor cortex (95.9%), primary somatosensory cortex (90.5%), premotor cortex (87.8%), hypothalamus (86.5%), posterior parietal cortex (75.7%), lateral prefrontal cortex (70.3%), ventromedial prefrontal cortex (51.4%), and orbitofrontal cortex (40.5%), respectively. These results suggest that the VN showed high connectivity with the cerebellum, thalamus, oculomotor nucleus, trochlear nucleus, abducens nucleus, and reticular formation, which are the brain regions related to the functions of the VN, including equilibrium, control of eye movements, conscious perception of movement, and spatial orientation.

Weber's syndrome, named after Hermann Weber, is characterized by midbrain lesions often caused by strokes, resulting in ipsilateral third nerve palsy, including ptosis and pupillary abnormalities, and contralateral hemiplegia. We discuss a case of a 35-year-old lady with cognitive impairment, right hemiparesis, diplopia, left eye ptosis, and lateral eye deviation. MRI of the brain with contrast suggested an acute infarct in the left-sided paramedian region of the midbrain. The oculomotor nucleus and cerebral peduncle were both affected by an abrupt left-sided paramedian midbrain stroke. The participation of particular midbrain nuclei together with symptoms including drooping eyelids, diplopia, and limb paralysis suggested Weber's syndrome. An MRI study of the brain is the modality of choice in suspected stroke cases and is more sensitive when it comes to the brainstem lesions. A comprehensive neurological examination with a clinical diagnosis of Weber's syndrome before radiological investigations is of great help for localizing brain stem lesions and thus aids in early diagnosis and treatment., Competing Interests: The authors have declared that no competing interests exist., (Copyright © 2024, Hatgaonkar et al.)

Lower motoneurons (MNs) show varied vulnerability in amyotrophic lateral sclerosis (ALS): those of non-ocular brainstem nuclei and most of those of the spinal cord are highly vulnerable, while those of extraocular brainstem nuclei are quite resistant. Results of our former study on the immunoexpression of the survival of motor neuron protein (SMN) and Gemins 2-4 in cervical spinal cord anterior horn α-MNs of sporadic ALS patients suggested that a relative deficit in Gemin2 may play some role in the pathomechanism of the disease. Here, we tested this idea further by comparing immunoexpression patterns of SMN and Gemins 2-8 between MNs of the oculomotor nucleus and α-MNs of the cervical spinal cord anterior horns in autopsy material from sALS patients and controls. In the latter, no considerable difference in any studied protein was found between these structures except that SMN expression was slightly but significantly lower (p < 0.01) in the oculomotor MNs. In the sporadic ALS patients, the expression of SMN, Gemin4 and Gemin7 was significantly weaker (p < 0.05, p < 0.05 and p < 0.01, respectively), while that of Gemin8 was stronger (p < 0.001) in the MNs of the oculomotor nucleus than in the examined cervical spinal cord anterior horn α-MNs. The immunoexpression of Gemin3 and Gemin6 in the spinal cord correlated strongly negatively with ALS duration (Spearman's correlation coefficient: RS = -0.84, p < 0.001, and RS = -0.86, p = 0.002, respectively). In the oculomotor nucleus MNs, no studied protein immunoexpression correlated significantly with ALS duration, but there was a tendency for such negative correlation for Gemin2 (RS = -0.56, p = 0.07). There was an apparent relative deficit of Gemin2 and Gemin8 in the spinal cord α-MNs and of Gemins 2, 4 and 7 in the oculomotor nucleus MNs. These data do not support the hypothesis that the diverse ALS vulnerability of the two MN subsets is related to their disparate expression patterns of SMN and Gemins 2-8. The differences in these patterns may result from ALS-related epiphenomena, or from intrinsic differences in the structure and function between the MN subsets, or both. [ABSTRACT FROM AUTHOR]

Several efforts have been made to understand the involvement of rapid eye movement (REM) sleep for cognitive processes. Consolidation or retention of recognition memories is severely disrupted by REM sleep deprivation (REMSD). In this regard, pedunculopontine tegmental nucleus (PPT) and other brainstem nuclei, such as pontine nucleus (Pn) and oculomotor nucleus (OCM), appear to be candidates to take part in this REM sleep circuitry with potential involvement in cognition. Therefore, the objective of this study was to investigate a possible association between the performance of Wistar rats in a declarative memory and PPT, Pn, and OCM activities after different periods of REMSD. We examined c-Fos and choline acetyltransferase (ChaT) expressions as indicators of neuronal activity as well as a familiarity-based memory test. The animals were distributed in groups: control, REMSD, and sleep rebound (REB). At the end of the different REMSD (24, 48, 72, and 96 h) and REB (24 h) time points, the rats were immediately tested in the object recognition test and then the brains were collected. Results indicated that OCM neurons presented an increased activity, due to ChaT-labeling associated with REMSD that negatively correlated ( r = −0.32) with the cognitive performance. This suggests the existence of a cholinergic compensatory mechanism within the OCM during REMSD. We also showed that 24 h of REMSD impacted similarly in memory, compared to longer periods of REMSD. These data extend the notion that REM sleep is influenced by areas other than PPT, i.e., Pn and OCM, which could be key players in both sleep processes and cognition. [ABSTRACT FROM AUTHOR]

Eye movements are generated by different premotor pathways. Damage to them can cause specific deficits of eye movements, such as saccades. For correlative clinico-anatomical post-mortem studies of cases with eye movement disorders it is essential to identify the functional cell groups of the oculomotor system in the human brain by marker proteins. Based on monkey studies, the premotor neurons of the saccadic system can be identified by the histochemical markers parvalbumin and perineuronal nets in humans. These areas involve the interstitial nucleus of Cajal (INC) and the rostral interstitial nucleus of the medial longitudinal fascicle (RIMLF), which both contain premotor neurons for upgaze and downgaze. Recent monkey and human studies revealed a selective excitatory calretinin-positive input to the motoneurons mediating upgaze, but not to those for downgaze. Three premotor regions were identified as sources of calretinin input in monkey: y-group, INC and RIMLF. These findings suggest that the expression pattern of parvalbumin and calretinin may help to identify premotor neurons involved in up- or downgaze. In a post-mortem study of five human cases without neurological diseases we investigated the y-group, INC and RIMLF for the presence of parvalbumin and calretinin positive neurons including their co-expression. Adjacent thin paraffin sections were stained for the aggrecan component of perineuronal nets, parvalbumin or calretinin and glutamate decarboxylase. The comparative analysis of scanned thin sections of INC and RIMLF revealed medium-sized parvalbumin positive neurons with and without calretinin coexpression, which were intermingled. The parvalbumin/calretinin positive neurons in both nuclei are considered as excitatory premotor upgaze neurons. Accordingly, the parvalbumin-positive neurons lacking calretinin are considered as premotor downgaze neurons in RIMLF, but may in addition include inhibitory premotor upgaze neurons in the INC as indicated by co-expression of glutamate decarboxylase in a subpopulation. Calretinin-positive neurons ensheathed by perineuronal nets in the human y-group are considered as the homologue premotor neurons described in monkey, projecting to superior rectus and inferior oblique motoneurons. In conclusion, combined immunostaining for parvalbumin, perineuronal nets and calretinin may well be suited for the specific identification and subsequent analysis of premotor upgaze pathways in clinical cases of isolated up- or downgaze deficits.

Eye movements are generated by different premotor pathways. Damage to them can cause specific deficits of eye movements, such as saccades. For correlative clinico-anatomical post-mortem studies of cases with eye movement disorders it is essential to identify the functional cell groups of the oculomotor system in the human brain by marker proteins. Based on monkey studies, the premotor neurons of the saccadic system can be identified by the histochemical markers parvalbumin (PAV) and perineuronal nets in humans. These areas involve the interstitial nucleus of Cajal (INC) and the rostral interstitial nucleus of the medial longitudinal fascicle (RIMLF), which both contain premotor neurons for upgaze and downgaze. Recent monkey and human studies revealed a selective excitatory calretinin (CR)-positive input to the motoneurons mediating upgaze, but not to those for downgaze. Three premotor regions were identified as sources of CR input in monkey: y-group, INC and RIMLF. These findings suggest that the expression pattern of parvalbumin and CR may help to identify premotor neurons involved in up- or downgaze. In a post-mortem study of five human cases without neurological diseases we investigated the y-group, INC and RIMLF for the presence of parvalbumin and CR positive neurons including their co-expression. Adjacent thin paraffin sections were stained for the aggrecan (ACAN) component of perineuronal nets, parvalbumin or CR and glutamate decarboxylase. The comparative analysis of scanned thin sections of INC and RIMLF revealed medium-sized parvalbumin positive neurons with and without CR coexpression, which were intermingled. The parvalbumin/CR positive neurons in both nuclei are considered as excitatory premotor upgaze neurons. Accordingly, the parvalbumin-positive neurons lacking CR are considered as premotor downgaze neurons in RIMLF, but may in addition include inhibitory premotor upgaze neurons in the INC as indicated by co-expression of glutamate decarboxylase in a subpopulation. CR-positive neurons ensheathed by perineuronal nets in the human y-group are considered as the homolog premotor neurons described in monkey, projecting to superior rectus (SR) and inferior oblique (IO) motoneurons. In conclusion, combined immunostaining for parvalbumin, perineuronal nets and CR may well be suited for the specific identification and subsequent analysis of premotor upgaze pathways in clinical cases of isolated up- or downgaze deficits. [ABSTRACT FROM AUTHOR]

Technical developments have extensively promoted experimental and clinical studies on cranial nerve regeneration, but intracranial nerve recovery is still an unexplored research area compared to peripheral nerve repair. In this study, we researched whether neurogenesis occurs in adult oculomotor (OMN) and Edinger-Westphal nucleus (EWN) or not after oculomotor nerve injury. To assess cell proliferation in response to unilateral oculomotor nerve crush (ONC) in adult beagle dog, repetitive 5-bromo-2′-deoxyuridine (BrdU) intravenous injections were performed during 3 or 7 days before the dogs were euthanized 2 h after the last injection on days 3, 7, 14, and 28 post-ONC. The proliferating cell types were investigated with three cell phenotypic markers and confocal microscopy on serial sections throughout the whole extent of OMN and EWN. BrdU-positive nuclei were detected in bilateral OMNs and EWNs from 3 to 28 days after ONC with the peak value at 3 days. Confocal analysis revealed that partial BrdU-positive cells colocalized with nestin or βIII-tubulin or GFAP, and the number of every kind of double-labeled cell maintained an increased tendency from 3 to 28 days post-ONC. Neither single-labeled BrdU-positive nuclei nor double-labeled cells were detected in the subependymal layer of cerebral aqueduct (SELCA) of all unilateral ONC dogs; also, they were not observed in the OMNs, EWNs, and SELCA of intact and sham-operated dog. These findings demonstrate that ONC can trigger continual mitotic activity, proliferation of NSCs, neurogenesis, and astrogliogenesis in the OMN and EWN of adult dogs. [ABSTRACT FROM AUTHOR]

Abstract: Objective: The ocular vestibular-evoked myogenic potential (oVEMP), a recently documented otolith-ocular reflex, is considered to reflect the central projections of the primary otolithic afferent fibers to the oculomotor nuclei. The aim of our study is to define air-conducted sound oVEMP abnormality in patients with acute brainstem lesions and to determine the brainstem structures involved in the generation of oVEMPs. Methods: In response to air-conducted tone burst sounds (ACS), oVEMP was measured in 52 patients with acute brainstem lesions. Individualized brainstem lesions were analyzed by means of MRI-based voxel-wise lesion-behavior mapping, and the probabilistic lesion maps were constructed. Results: More than half (n =28, 53.8%) of the patients with acute brainstem lesions showed abnormal oVEMP in response to ACS. The majority of patients with abnormal oVEMPs had lesions in the dorsomedial brainstem that contains the medial longitudinal fasciculus (MLF), the crossed ventral tegmental tract (CVTT), and the oculomotor nuclei and nerves. Conclusion: MLF, CVTT, and the oculomotor nuclei and nerves appear to be responsible for otolith-ocular responses in the brainstem. Significance: Complemented to cervical VEMP for the uncrossed otolith-spinal function, oVEMP to ACS may be applied to evaluate the crossed otolith-ocular function in central vestibulopathies. [Copyright &y& Elsevier]

Comprehension of the mesencephalic syndromes that affect oculomotor nerve fascicles requires a detailed knowledge of their relationship with the adjacent structures and the blood supply of the central midbrain region. This was the reasoning behind our study, which was performed in ten serially sectioned midbrains stained with cresyl violet and luxol fast blue, in three microdissected midbrains, and in two injected and cleared specimens. Three continuous groups of the intramesencephalic oculomotor nerve fascicles were distinguished: the caudal, intermediate and rostral. The caudal fascicles, which most likely innervate the superior rectus and the levator palpebrae superioris muscles, extend through the superior cerebellar peduncle just caudal to the red nucleus and close to the lateral lemniscus. The intermediate fascicles, devoted to the medial rectus and the inferior oblique muscles, always pass through the superior cerebellar peduncle, just medial to the caudal part of the red nucleus (60 %), and less frequently (40 %) through the nucleus itself. The rostral oculomotor fascicles, which terminate in the inferior rectus and sphincter pupillae muscles, course medial to the rostral part of the red nucleus. While the rostral and intermediate oculomotor fascicles are supplied only by the medial twigs of the paramedian mesencephalic perforating arteries, the caudal fascicles are also nourished by the lateral branches of the same perforating arteries. The data obtained form an important basis for the explanation of certain mesencephalic syndromes, and even anticipate some new syndromes not yet described in the literature. [ABSTRACT FROM AUTHOR]

Post-traumatic stress disorder (PTSD) is an anxiety disorder that develops after exposure to a life-threatening traumatic experience. Mental disorder appears after the traumatic stress incident and affects the movement of the eye muscle dominated by the oculomotor nucleus, an important nuclear group of the brainstem. It has been reported that dysfunction of the neurotransmitter 5-hydroxytryptamine (5-HT) can lead to the instability of the internal environment in response to stress and plays an important role in the pathology of PTSD and that the 5-HT1A receptor (5-HT1AR) is critically involved in regulating mood and anxiety levels. In this study, the 5-HT1AR expression in the oculomotor nucleus was examined in rats with single-prolonged stress (SPS), a well established post-traumatic stress disorder animal model. Our results show that the expression of 5-HT1AR in the oculomotor nucleus neurons gradually increased 1, 4, and 7 days after exposure to SPS in comparison to the normal control group, measured by immunohistochemistry, western blotting, and reverse transcription polymerase chain reaction (RT-PCR). The expression of 5-HT1AR reached its peak 7 days after the SPS exposure and then decreased 14 days after. There is also a change in the ultrastructure in the oculomotor nucleus neuron upon SPS treatment which was observed by transmission electron microscopy. These results suggest that SPS can induce a change of the 5-HT1AR expression in the oculomotor nucleus, which may be one of the molecular mechanisms that lead to PTSD. [ABSTRACT FROM AUTHOR]

Palisade endings (PEs), which are unique to the eye muscles, are associated with multiply innervated muscle fibers. They lie at the myotendinous junctions and form a cap around the muscle fiber tip. They are found in all animals investigated so far, but their function is not known. Recently, we demonstrated that cell bodies of PEs and tendon organs lie around the periphery of the oculomotor nucleus in the C- and S-groups. A morphological analysis of these peripheral neurons revealed the existence of different populations within the C-group. We propose that a small group of round or spindle-shaped cells gives rise to PEs, and another group of multipolar neurons provide the multiple motor endings. If PEs have a sensory function, then their cell body location close to motor neurons would be in an ideal location to control tension in extraocular muscles; in the case of the C-group, its proximity to the preganglionic neurons of the Edinger-Westphal nucleus would permit its participation in the near response. Despite their unusual properties, PEs may have a sensory function. [ABSTRACT FROM AUTHOR]

Recent monkey studies showed that motoneurons of the oculomotor nucleus involved in upward eye movements receive a selective input from afferents containing calretinin (CR). Here, we investigated the sources of these CR-positive afferents. After injections of tract-tracers into the oculomotor nucleus (nIII) of two monkeys, the retrograde labeling was combined with CR-immunofluorescence in frozen brainstem sections. Three sources of CR inputs to nIII were found: the rostral interstitial nucleus of the medial longitudinal fascicle (RIMLF), the interstitial nucleus of Cajal, and the y-group. CR is not present in all premotor upward-moving pathways. The excitatory secondary vestibulo-ocular neurons in the magnocellular part of the medial vestibular nuclei contained nonphosphorylated neurofilaments, but no CR, and they received a strong supply of large CR-positive boutons. In conclusion, the present study presents evidence that only specific premotor pathways for upward eye movements-excitatory upgaze pathways-contain CR, but not the up vestibulo-ocular reflex pathways. This property may help to differentiate between premotor up- and downgaze pathways in correlative clinico-anatomical studies in humans. [ABSTRACT FROM AUTHOR]

For a given eye position, firing rates of abducens neurons (ABNs) generally (Mays et al. 1984), and lateral rectus (LR) motoneurons (MNs) in particular (Gamlin et al. 1989a), are higher in converged gaze than when convergence is relaxed, whereas LR and medial rectus (MR) muscle forces are slightly lower (Miller et al. 2002). Here, we confirm this finding for ABNs, report a similarly paradoxical finding for neurons in the MR subdivision of the oculomotor nucleus (MRNs), and, for the first time, simultaneously confirm the opposing sides of these paradoxes by recording physiological LR and MR forces. Four trained rhesus monkeys with binocular eye coils and custom muscle force transducers on the horizontal recti of one eye fixated near and far targets, making conjugate saccades and symmetric and asymmetric vergence movements of 16-27°. Consistent with earlier findings, we found in 44 ABNs that the slope of the rate-position relationship for symmetric vergence (kV) was lower than that for conjugate movement (kC) at distance, i.e., mean kV/kC = 0.50, which implies stronger LR innervation in convergence. We also found in 39 MRNs that mean kV/kC = 1.53, implying stronger MR innervation in convergence as well. Despite there being stronger innervation in convergence at a given eye position, we found both LR and MR muscle forces to be slightly lower in convergence, -0.40 and -0.20 g, respectively. We conclude that the relationship of ensemble MN activity to total oculorotary muscle force is different in converged gaze than when convergence is relaxed. We conjecture that LRMNs with kV < kC and MRMNs with kV > kC innervate muscle fibers that are weak, have mechanical coupling that attenuates their effective oculorotary force, or serve some nonoculorotary, regulatory function. [ABSTRACT FROM AUTHOR]

In all vertebrates, including humans, the Edinger–Westphal nucleus (EW) forms a circumscribed cell group dorsomedial to the oculomotor nucleus (nIII). Traditionally the EW is considered the location of parasympathetic preganglionic neurons of the ciliary ganglion, mediating pupillary constriction and accommodation. In a comparative study in rat, ferret, monkey, and human, the location of cholinergic neurons within and around the nIII, which includes motoneurons of the extra-ocular muscles and the preganglionic neurons of the ciliary ganglion, was compared to the location of urocortin-positive neurons. Irrespective of the species, the cholinergic and urocortin-positive neurons form largely separated cell populations adjacent to each other. Only in monkey, cholinergic putative preganglionic neurons were found within the cytoarchitecturally defined EW, whereas in rat, ferret, and human the EW is almost exclusively composed of urocortin-positive neurons. In humans, the presumed preganglionic neurons are located as an inconspicuous group of choline acetyltransferase-positive neurons dorsal to the urocortin-positive EW. [ABSTRACT FROM AUTHOR]